An image capturing apparatus such as a digital camera which captures an image by converting an image signal into an electrical signal receives an image capturing light beam using an image sensor, converts the photo-electrically converted signal output from the image sensor into image data, and records the resultant image data on a recording medium such as a memory card. A CCD (Charge Coupled Device) or C-MOS (Complementary Metal Oxide Semiconductor) is known as the image sensor.
In such an image capturing apparatus, an optical low-pass filter and infrared cut filter are arranged on the object side of the image sensor. It has been known that when foreign substances such as dust adhere to the surfaces of these filters or a cover glass of the image sensor, the adhesion portion is seen in a captured image as a black point to result in degradation in its quality.
Especially in a interchangeable single-lens reflex digital camera, since mechanical actuating units such as a shutter or quick return mirror are set near the image sensor, foreign substances such as dust produced from these actuating units sometimes adhere on the image sensor or low-pass filter. Also, dust or the like sometimes enters the camera main body from the opening of the lens mount and adheres on it (what is it?) during lens interchange.
As a prior art for solving the above problem, Japanese Patent Laid-Open No. 2002-204379 discloses a technique for providing, on the object side of the image sensor, a dustproof curtain which transmits an image capturing light beam, to cause a piezoelectric element to vibrate the dustproof curtain, thereby removing the foreign substance such as dust adhering to the surface of the dustproof curtain.
Japanese Patent Laid-Open No. 2003-330082 discloses a technique for executing the vibration operation for removing a foreign substance such as dust after activating the system upon power ON, upon attaching/detaching the lens or accessory unit, or prior to a release (image capturing) operation.
Japanese Patent Laid-Open No. 2004-264580 discloses a technique for changing the vibration mode of the vibration operation for removing a foreign substance such as dust, between a timing synchronized with a release (image capturing) operation and a timing corresponding to manual operation or lens attachment/detachment.
To remove the foreign substance adhering to the surface of the dustproof curtain, Japanese Patent Laid-Open No. 2002-204379 described above applies a voltage to the piezoelectric element which connects to the dustproof curtain, to vibrate the dustproof curtain by driving the piezoelectric element. In this case, removal of the foreign substance adhering to the dustproof curtain requires scattering the foreign substance from the dustproof curtain by applying a force stronger than the adhesion force of the foreign substance to it, so large energy is necessary. However, Japanese Patent Laid-Open No. 2002-204379 does not consider any method of efficiently driving the piezoelectric element to effectively remove the foreign substance when vibrating the dustproof curtain. This leads to high power consumption.
Japanese Patent Laid-Open No. 2003-330082 executes the vibration operation for removing a foreign substance such as dust not only when vibrating the dustproof curtain after activating the system upon power ON and when attaching/detaching the lens or accessory unit but also for every release operation. Therefore, the influence of power supply energy consumed by vibrating the dustproof curtain on the number of photographable images is not negligible.
Japanese Patent Laid-Open No. 2004-264580 executes the vibration operation for removing a foreign substance such as dust in a low power consumption mode only at a slow shutter speed or only for the valve in a release operation at a timing other than that corresponding to manual operation or lens attachment/detachment. However, the vibration operation with low power consumption, i.e., the vibration operation with low foreign substance removal capability sometimes fails to sufficiently remove the dust. This may only result in wasteful power consumption.
Both of the above-described prior arts execute the vibration operation for removing a foreign substance such as dust in lens interchange. Actually, a foreign substance such as dust in the outside air can readily enter the mirror box in lens interchange because the mount opens and the interior of the mirror box is exposed to the outside air.
However, even when a foreign substance such as dust enters the mirror box at this time, it merely adheres to the wall surface or structure in the mirror box in many cases. Therefore, the foreign substance rarely enters the region beyond the shutter curtain while it is closed. That is, while the shutter curtain is closed, a foreign substance rarely adheres to the surface of the optical member such as a filter which covers the image sensor unit. It is not always good to execute the vibration operation for removing a foreign substance such as dust in lens interchange.
Various references reveal that the foreign substance such as dust adhering on the optical member such as a filter strongly produces an adhesion force using, e.g., Van der Waals force, liquid cross-linking force, and electrostatic force. As measures against the adhesion due to an electrostatic force, there have been known a variety of techniques for, e.g., making the surface of the optical member such as a filter fall to GND to drop the surface potential, thereby removing the charges of the surface and preventing charging of the surface.
Various kinds of foreign substances such as dust adhere on the optical member such as a filter. It has been clarified by experiments that when a foreign substance is left adhered for a long period of time, its adhesion force generally increases and makes it hard to remove the foreign substance. This phenomenon occurs because the adhesion force such as a liquid cross-linking force increases as the foreign substance condenses upon a change in environment, i.e., temperature/humidity, or because the foreign substance gets stronger adhesion as the dirt repeatedly swells and dries upon a change in temperature/humidity. Also, an elastic material such as rubber gets stronger adhesion because fat and oil contained in itself bleed over time.
The present invention has been made in consideration of the above problems, and has as its object to more efficiently remove, at a more effective timing, a foreign substance such as dust adhering on an optical member inserted on the image capturing optical axis.